2.'iS riiinrsitu of ('(ilifoniia I'liblicatioiis hi Ztmhxjt) [Vol.15 



1915, pp. 127-132) were also used, especially in the region west of 

 Los Coronados (or the Coronado Islands, pi. 4). Here our intensive 

 explorations made possible a more detailed representation of the to- 

 pography. Though but few soundings have been made more than ten 

 miles off shore, it is improbable that future explorations will neces- 

 sitate any important alteration of the contours. 



The contour maps reveal the presence of numerous submerged 

 valleys and other regions where the depth increases rapidly. In fact, 

 depths exceeding a thousand meters are usually found within fifty 

 miles of the coast, and depths exceeding five hundred meters occur in 

 several regions within five miles of the coast. For a detailed discus- 

 sion of the submei-ged valleys and other topographic features of the 

 ocean bottom off California and Mexico, the reader is referred to 

 Davidson (1897). 



B. HORIZONTAL DISTRIBUTION OF TEMPERATURES AND 

 SALINITIES 



1. Surface Isotherms and Isohalines in Several Large Areas 

 (a) Some general principles underlying oceanic circulation. — 

 Samples of ocean water taken at different times from the same posi- 

 tion, or from different positions at the same time, usually differ in 

 one or more respects, e.g., in temperature, salinity, gas content, etc. 

 Such differences are of course due to variations in the wind, humidity 

 of the air, solar radiation, etc., and to the flow of the water. ' 



Furtliermore, water having certain properties often flows as a 

 current or slow drift into regions where the local conditions tend to 

 produce different properties. For example, water flowing from a 

 region where a certain intensity of solar radiation prevails into one 

 of greater intensity is colder than the neighboring still water. And, 

 in general, the presence at any place of water differing significantly 

 in any property from that corresponding to local conditions indicates 

 a flow of water from a region where different conditions prevail. 



Any difference in the properties of the water that changes its 

 density tends to give rise to a convective circulation. If acting alone, 

 this circulation would result in a series of layers of water which, 

 while increasing in density in situ with the depth, would not vary in 

 density with respect to horizontal distances. In addition, tliere is 



